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| United States Patent |
5,517,646
|
|
Piccirillo
, et al.
|
May 14, 1996
|
Expansion device configuration system having two configuration modes
which uses automatic expansion configuration sequence during first mode
and configures the device individually during second mode
Abstract
A circuit for configuring a Plug and Play expansion card in one of three
ways. The first is the standard Plug and Play configuration method,
wherein expansion cards go through the isolation process to obtain unique
Card Select Numbers (CSN). This method requires the existence of a
dedicated serial EEPROM to store the system resource data for the
expansion cards. However, when an expansion card is directly mounted onto
a system board, it becomes a system board device. This allows the separate
serial EEPROM to be removed. To implement, two alternative configuration
modes are provided, wherein the expansion card can be configured under
main CPU control. In these alternative modes, the configuration data is
stored in the main system BIOS ROM. In the first mode, a register in the
expansion card is mapped to a fixed ISA I/O address. In the second mode,
the register is controlled by a dedicated pin, thus allowing it to be
mapped to any ISA I/O address. To determine which configuration mode is
used by the expansion card, pullup or pulldown resistors are connected to
certain expansion card output pins. A second embodiment is also described
wherein a static random access memory (SRAM) is utilized to store the
serial identifier and the resource data. In this embodiment, the system
BIOS initially writes the serial identifier and resource data into the
SRAM. After this is done, a Plug and Play configuration process is
invoked, in which the serial identifier is retrieved from the SRAM rather
than the serial EEPROM.
| Inventors:
|
Piccirillo; Gary J. (Houston, TX);
Welker; Mark W. (Spring, TX);
Thayer; John S. (Houston, TX)
|
| Assignee:
|
Compaq Computer Corp. (Houston, TX)
|
| Appl. No.:
|
233032 |
| Filed:
|
April 25, 1994 |
| Current U.S. Class: |
713/1; 710/10 |
| Intern'l Class: |
G06F 013/00; G06F 009/00 |
| Field of Search: |
395/700,725,775,800,575,500,325,200,200.01
|
References Cited
U.S. Patent Documents
| 4373181 | Feb., 1983 | Chrisholm et al. | 395/400.
|
| 4578773 | Mar., 1986 | Desai et al. | 395/275.
|
| 4750136 | Jun., 1988 | Arpin et al. | 364/514.
|
| 4760553 | Jul., 1988 | Buckley et al. | 364/900.
|
| 4800302 | Jan., 1989 | Marum | 326/10.
|
| 5038320 | Aug., 1991 | Heath et al. | 364/900.
|
| 5111423 | May., 1992 | Kopec, Jr. et al. | 395/500.
|
| 5161102 | Nov., 1992 | Griffin et al. | 395/800.
|
| 5247682 | Sep., 1993 | Kondou et al. | 395/700.
|
| 5257387 | Oct., 1993 | Richek et al. | 395/800.
|
| 5317750 | May., 1994 | Wickersheim et al. | 395/725.
|
| 5329634 | Jul., 1994 | Thompson | 395/500.
|
| 5367640 | Nov., 1994 | Hamilton et al. | 395/827.
|
| 5379431 | Jan., 1995 | Lemon et al. | 395/700.
|
| 5418960 | May., 1995 | Munroe | 395/700.
|
Other References
Jonathan Cassell; "Electronic Buyers News" Nov. 15, 1993, p. 60.
Plug and Play ISA Specification, Version 1.02, pp. 4-25, 27-28, 51-53,
60-64, (Mar. 15, 1994).
Plug and Play BIOS Specification, Version 1.0A, pp. 4-27, 38-46, (Mar. 10,
1994).
|
Primary Examiner: An; Meng-Ai
Attorney, Agent or Firm: Pravel, Hewitt, Kimball & Krieger
Claims
We claim:
1. An improved expansion bus device for use with a computer system having
both said improved expansion bus device and other expansion bus devices,
wherein the computer system can obtain device specific initialization
information from the other expansion bus devices which individually
include a nonvolatile storage device for storing such initialization
information and wherein the computer system provides configuration
information to both said improved expansion bus device and to said other
expansion bus devices based on the initialization information according to
a predetermined automatic expansion configuration sequence, and wherein
the computer system can further store appropriate configuration
information on the improved expansion bus device and provide the
configuration information to the improved expansion bus device without
utilizing said predetermined automatic expansion configuration sequence,
said improved expansion bus device having first and second configuration
modes, wherein a non-volatile storage device for storing said
initialization information is connected to said improved expansion bus
device for configuration mode operation, said improved expansion bus
device comprising:
means for determining said first configuration mode and said second
configuration mode for said improved expansion bus device;
means for storing the configuration information of said improved expansion
bus device received from the computer system;
means responsive to said first configuration mode for retrieving said
initialization information from the non-volatile storage device and
providing said initialization information to the computer system and for
receiving the configuration information from the computer system and
storing the configuration information in said configuration storing means,
said means responsive to said first configuration mode responding
according to the predetermined automatic expansion configuration sequence;
and
means responsive to said second configuration mode for receiving the
configuration information from the computer system and storing the
configuration information in said configuration storing means without
providing said initialization information to the computer system, said
means responsive to said second configuration mode responding without
following the predetermined automatic expansion configuration sequence,
said means responsive to said second configuration mode including a
register settable to an active state by the computer system to enable
receipt of the configuration information and being responsive to a fixed
address.
2. The expansion bus device of claim 1, wherein said configuration
information storing means includes a plurality of registers.
3. The expansion bus device of claim 1, wherein the predetermined automatic
expansion configuration sequence is defined according to the Plug and Play
standard.
4. An improved expansion bus device for use with a computer system having
both said improved expansion bus device and other expansion bus device,
wherein the computer system can obtain device specific initialization
information from the other expansion bus devices which individually
include a non-volatile storage device for storing such initialization
information and wherein the computer system provides configuration
information to both said improved expansion bus device and to said other
expansion bus devices based on the initialization information according to
a predetermined automatic expansion configuration sequence and wherein the
computer system can further store initialization information on the
improved expansion bus device and provide the initialization information
to the improved expansion bus device prior to utilizing said predetermined
automatic expansion configuration sequence and wherein the computer system
including non-volatile memory for storing system BIOS information and
wherein said initialization information is stored in said non-volatile
memory, said improved expansion bus device having first and second
configuration modes, wherein a non-volatile storage device for storing
said initialization information is connected to said improved expansion
bus device for first configuration mode operation, said improved expansion
bus device comprising:
means for determining said first configuration mode and said second
configuration mode;
a volatile storage device for storing the initialization information
received from the computer system;
means for storing the configuration information of the improved expansion
bus device received from the computer system;
means responsive to said first configuration mode for retrieving said
initialization information from said non-volatile storage device and
providing said initialization information to the computer system and for
receiving the configuration information from the computer system and
storing the configuration information in said configuration information
storing means, said means responsive to said first configuration mode
responding according to the predetermined automatic expansion
configuration sequence; and
means responsive to said second configuration mode for receiving said
initialization information from the computer system and storing said
initialization information in said volatile storage device, and for
retrieving said initialization information from said volatile storage
device and providing said initialization information to the computer
system and also for receiving the configuration information from the
computer system and storing the configuration information in said
configuration information storing means, said means responsive to said
second configuration mode responding according to the predetermined
automatic expansion configuration sequence after receiving said
initialization information from the computer system, wherein said means
responsive to said second configuration mode is responsive to a fixed
address.
5. The expansion bus device of claim 4, wherein said configuration
information storing means includes a plurality of registers.
6. The expansion bus device of claim 4, wherein said volatile storage
device is a static random access memory.
7. The expansion bus device of claim 4, wherein the predetermined automatic
expansion configuration sequence is defined according to the Plug and Play
standard.
8. An improved expansion bus device for use with a computer system having
both said improved expansion bus device and other expansion bus device,
wherein the computer system can obtain device specific initialization
information from the other expansion bus devices which individually
include a non-volatile storage device for storing such initialization
information and wherein the computer system provides configuration
information to both said improved expansion bus device and to said other
expansion bus devices based on the initialization information according to
a predetermined automatic expansion configuration sequence and wherein the
computer system can further store initialization information on the
improved expansion bus device and provide the initialization information
to the improved expansion bus device prior to utilizing said predetermined
automatic expansion configuration sequence and wherein the computer system
includes non-volatile memory for storing system BIOS information and
wherein said initialization information is stored in said non-volatile
memory, said improved expansion bus device comprising:
a volatile storage device for storing the initialization information
received from the computer system;
means for storing the configuration information of the improved expansion
bus device received from the computer system; and
means for receiving said initialization information from the computer
system and storing said initialization information in said volatile
storage device, and for retrieving said initialization information from
said volatile storage device and providing said initialization information
back to the computer system and also for receiving the configuration
information from the computer system and storing the configuration
information in said configuration information storing means, said means
for receiving responding according to the predetermined automatic
expansion configuration sequence after receiving said initialization
information from the computer system wherein said means for receiving said
initialization information is responsive to a fixed address.
9. The expansion bus device of claim 8, wherein said configuration
information storing means includes a plurality of registers.
10. The expansion bus device of claim 8, wherein said volatile storage
device is a static random access memory.
11. The expansion bus device of claim 8, wherein the predetermined
automatic expansion configuration sequence is defined according to the
Plug and Play standard.
12. An improved expansion bus device for use with a computer system having
both said improved expansion bus device and other expansion bus devices,
wherein the computer system can obtain device specific initialization
information from the other expansion bus devices which individually
include a non-volatile storage device for storing such initialization
information and wherein the computer system provides configuration
information to both said improved expansion bus device and to said other
expansion bus devices based on the initialization information according to
a predetermined automatic expansion configuration sequence, and wherein
the computer system can further store appropriate configuration
information on the improved expansion bus device and provide the
configuration information to the improved expansion bus device without
utilizing said predetermined automatic expansion configuration sequence,
said improved expansion bus device having first and second configuration
modes, wherein a non-volatile storage device for storing said
initialization information is connected to said improved expansion bus
device for first configuration mode operation, said improved expansion bus
device comprising:
means for determining said first configuration mode and said second
configuration mode for said improved expansion bus device;
means for storing the configuration information of said improved expansion
bus device received from the computer system;
means responsive to said first configuration mode for retrieving said
initialization information from the non-volatile storage device and
providing said initialization information to the computer system and for
receiving the configuration information from the computer system and
storing the configuration information in said configuration storing means,
said means responsive to said first configuration mode responding
according to the predetermined automatic expansion configuration sequence;
and
means responsive to said second configuration mode for receiving the
configuration information from the computer system and storing the
configuration information in said configuration storing means without
providing said initialization information to the computer system, said
means responsive to said second configuration mode responding without
following the predetermined automatic expansion configuration sequence,
said means responsive to said second configuration mode including a
register settable to an active state by the computer system to enable
receipt of the configuration information and being responsive to a chip
select signal from the computer system.
13. The improved expansion bus device of claim 12, wherein said
configuration information storing means includes a plurality of registers.
14. The improved expansion bus device of claim 12, wherein the
predetermined automatic expansion configuration sequence is defined
according to the Plug and Play standard.
15. An improved expansion bus device for use with a computer system having
both said improved expansion bus device and other expansion bus devices,
wherein the computer system can obtain device specific initialization
information from the other expansion bus devices which individually
include a non-volatile storage device for storing such initialization
information and wherein the computer system provides configuration
information to both said improved expansion bus device and to said other
expansion bus devices based on the initialization information according to
a predetermined automatic expansion configuration sequence, and wherein
the computer system can further store appropriate configuration
information on the improved expansion bus device and provide the
configuration information to the improved expansion bus device without
utilizing said predetermined automatic expansion configuration sequence
and wherein the computer system includes non-volatile memory for storing
system BIOS information and wherein said initialization information is
stored in said non-volatile memory, said improved expansion bus device
having first and second configuration modes, wherein a non-volatile
storage device for storing said initialization information is connected to
said improved expansion bus device for first configuration mode operation,
said improved expansion bus device comprising:
means for determining said first configuration mode and said second
configuration mode for said improved expansion bus device;
a volatile storage device for storing the initialization information
received from the computer system;
means for storing the configuration information of said improved expansion
bus device received from the computer system;
means responsive to said first configuration mode for retrieving said
initialization information from the non-volatile storage device and
providing said initialization information to the computer system and for
receiving the configuration information from the computer system and
storing the configuration information in said configuration storing means,
said means responsive to said first configuration mode responding
according to the predetermined automatic expansion configuration sequence;
and
means responsive to said second configuration mode for receiving said
initialization information from the computer system and storing said
initialization information in said volatile storage device, and for
retrieving said initialization information from said volatile storage
device and providing said initialization information to the computer
system and also for receiving the configuration information from the
computer system and storing the configuration information in said
configuration information storing means, said means responsive to said
second configuration mode responding according to the predetermined
automatic expansion configuration sequence after receiving said
initialization information from the computer system, wherein said means
responsive to said second configuration mode is responsive to a chip
select signal from the computer system.
16. The improved expansion bus device of claim 15, wherein said
configuration information storing means includes a plurality of registers.
17. The improved expansion bus device of claim 15, wherein said volatile
storage device is a static random access memory.
18. The improved expansion bus device of claim 15, wherein said means
responsive to said second configuration mode includes a register settable
to an active state by the computer system to enable receipt of the
configuration information.
19. An improved expansion bus device for use with a computer system having
both said improved expansion bus device and other expansion bus device,
wherein the computer system can obtain device specific initialization
information from the other expansion bus devices which individually
include a non-volatile storage device for storing such initialization
information and wherein the computer system provides configuration
information to both said improved expansion bus device and to said other
expansion bus devices based on the initialization information according to
a predetermined automatic expansion configuration sequence and wherein the
computer system can further store initialization information on the
improved expansion bus device and provide the initialization information
to the improved expansion bus device prior to utilizing said predetermined
automatic expansion configuration sequence and wherein the computer system
includes non-volatile memory for storing system BIOS information and
wherein said initialization information is stored in said non-volatile
memory, said improved expansion bus device comprising:
a volatile storage device for storing the initialization information
received from the computer system;
means for storing the configuration information of the improved expansion
bus device received from the computer system; and
means for receiving said initialization information from the computer
system and storing said initialization information in said volatile
storage device, and for retrieving said initialization information from
said volatile storage device and providing said initialization information
back to the computer system and also for receiving the configuration
information from the computer system and storing the configuration
information in said configuration information storing means, said means
for receiving responding according to the predetermined automatic
expansion configuration sequence after receiving said initialization
information from the computer system, wherein said means for receiving the
initialization information is responsive to a chip select signal from the
computer system.
20. The improved expansion bus device of claim 19, wherein said
configuration information storing means includes a plurality of registers.
21. The improved expansion bus device of claim 19, wherein said volatile
storage device is a static random access memory.
22. The improved expansion bus device of claim 19, wherein the
predetermined sequence is defined according to the Plug and Play standard.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the configuration of expansion devices, and more
particularly, to a technique of configuring the expansion devices without
the need for a separate storage device.
2. Description of the Related Art
The most popular expansion bus standard in the PC industry today is the
Industry Standard Architecture (ISA). The ISA bus was first used in the
PC/AT line of personal computers by International Business Machines
Corporation (IBM). As a result of the immense popularity of ISA, a large
number (thousands) of expansion cards and peripherals are available for
ISA compatible personal computers. The ISA bus requires the allocation of
memory and I/O address spaces, DMA channels and interrupt levels among
multiple ISA expansion cards. However, ISA does not define a hardware or
software mechanism for allocating these resources. Consequently,
configuration of ISA cards is typically done with switches or jumpers that
change the decode maps for memory and I/O space and steer the DMA and
interrupt signals to different pins on the bus. In addition, system
configuration files need to be updated to reflect the configuration
changes. When more than one expansion card is placed onto an ISA bus,
conflicts may arise as a result of the different resource requirements of
the expansion cards. To address these potential conflicts, users had to
refer to documentation provided by the expansion card manufactures. For
the user, this configuration process was both time consuming and
unreliable.
In a joint effort between Compaq Corporation, Intel Corporation, Microsoft
Corporation and Phoenix Technologies Ltd., the Plug and Play standard was
developed. The Plug and Play specification allows for the automatic
configuration of Plug and Play expansion cards. Any conflict that may
exist between different Plug and Play cards is automatically resolved by
the system. In systems where both Plug and Play expansion cards and
standard ISA cards are connected, the configuration needs to be augmented
in the system BIOS and/or operating system to manage and arbitrate ISA bus
resources.
The two key functions performed by the Plug and Play system BIOS are
resource management and runtime configuration. The basic system resources,
which include the DMA channels, interrupt request lines, and I/O and
memory addresses, are allocated by the Plug and Play system BIOS in its
resource management mode. Because there are thousands of expansion cards
available, these system resources are commonly allocated in a conflicting
manner in ISA systems, which can lead to bootstrap and system
configuration failures. In its role as resource manager, the Plug and Play
system BIOS configures the Plug and Play expansion cards before or during
the Power On Self Test (POST) procedure. The main system board and other
standard ISA cards are configured during the POST procedure. It is noted
that the Plug and Play system BIOS performs the same POST requirements of
existing ISA computer systems. During the Plug and Play configuration
phase, the Plug and Play expansion cards provide their resource
requirements to allow the system BIOS to perform resource allocation and
conflict resolution. After the configuration procedure is complete, POST
is executed. After the POST procedure is completed, control is transferred
from the system BIOS to the operating system software. However, in its
runtime configuration mode, the system BIOS does provide configuration
services for system board devices after the POST procedure has finished.
This feature allows the system BIOS to dynamically change the resources
allocated to system board devices after the operating system has been
loaded thereby allow the operating system software to manipulate the
configuration of the system board devices.
A more detailed description of the procedure for configuring Plug and Play
ISA expansion cards would be clearer when discussed in conjunction with
FIGS. 1 and 2. Referring now to FIG. 1, the configuration steps executed
by the Plug and Play system BIOS for Plug and Play expansion cards are
shown. Upon power-up, all Plug and Play expansion cards detect a signal
RESET.sub.-- DRV, which is asserted by a reset controller in the computer
system during power-up to cause a hardware reset of the ISA expansion
boards. Upon detection of the asserted signal RESET.sub.-- DRV, the Plug
and Play expansion cards set their card select number (CSN) to the value
0, and enter into a WAIT FOR KEY state. The commands asserted by the
system BIOS to the Plug and Play expansion cards are provided through
three 8-bit I/O ports: an ADDRESS port, a WRITE.sub.-- DATA port and a
READ.sub.-- DATA port. The expansion cards in the WAIT FOR KEY state do
not respond to any access to their ports until an initiation key is
detected. The initiation key is defined by a series of writes to the
ADDRESS port of each expansion card. In step 100, if the proper series of
I/O writes performed by the system BIOS is decoded, then the Plug and Play
expansion cards enter into a configuration mode. Once in configuration
mode, the cards enter into a SLEEP state. Proceeding now to step 104, a
command WAKE[CSN] is asserted with the value of CSN equal to 0. This
causes the expansion cards to transition from the SLEEP state to an
ISOLATION state, and to initialize a serial identifier/resource data
pointer. Because all of the expansion cards respond to the same I/O port
addresses, a unique number provided on each card is used to distinguish
the Plug and Play expansion cards. This unique number is also referred to
as the serial identifier, which is a 72-bit number composed of two 32-bit
fields and an 8-bit checksum. The first 32-bit field is typically the
vendor identifier, while the second 32-bit field can be any value, such as
the card serial number, as long as the first and second 32-bit fields
represent a number that is unique to that expansion card. The 8-bit
checksum is used to ensure that no conflicts have occurred while reading
the device identifier information. Each expansion card writes its serial
identifier into a serial isolation register, whose contents are outputted
one bit at a time. After the expansion card has been properly placed into
the ISOLATION state, control proceeds to step 106, where the expansion
cards are isolated in an isolation process. Step 106 is shown in more
detail in FIG. 2.
Referring now to FIG. 2, a flow diagram of the Plug and Play ISA expansion
card isolation is shown. Each expansion card expects 72 pairs of I/O read
accesses to the READ.sub.-- DATA port. Each expansion card responds to
these reads depending on the value of each bit of the 72-bit serial
identifier, which is serially outputted one bit at a time, starting at the
least significant bit of the serial identifier. In step 200, the first bit
is obtained from the serial isolation register. Next, in step 202, it is
determined if the current bit of the serial identifier is a 1. If so, the
expansion card writes the value 0.times.55 onto a data bus SD[7:0] in step
204. It is noted that more than one expansion card can drive the data bus
SD[7:0] with the value 0.times.55 at the same time. If the current bit of
the serial identifier is a 0, then control proceeds to step 206, where the
expansion card(s) tristate the output drivers connected to data bus
SD[7:0]. For those expansion cards whose current serial identifier bit is
0, control next proceeds from step 206 to step 208, where the expansion
card(s) determine if the data bus SD[1:0] is equal to the binary value 01.
If so, that would indicate that at least one other expansion card on the
ISA bus is driving the value 0.times.55 onto the data bus D[7:0]. Control
stays in step 208 until a second I/O read is performed to the same
location in the serial isolation register. Thus, for each bit in the
serial isolation register, two reads are performed on that bit. Each of
these two reads is referred to as a phase of the isolation register read
cycle during the isolation process. When the second read occurs, control
proceeds from step 208 to step 212 for those expansion card(s) where the
current serial identifier bit is equal to zero. If in step 208 it is
determined that the data bus SD[1:0] is not equal to the binary value 01,
then control proceeds to step 214 when the second I/O read occurs. For
these particular expansion cards, their output drivers remain tristated.
For the expansion card(s) whose current serial identifier bit is a 1,
control proceeds from step 204 to step 210 when the second I/O read
occurs. In step 210, the expansion card(s) that drove the value
0.times.55 onto the data bus SD[7:0] in step 204 now drive the value
0.times.AA onto the data bus SD[7:0]. In step 212, the expansion card(s)
with the tristated data outputs determines if the data bus SD[1:0]
contains the binary value 10. If so, control proceeds to step 216. This
indicates that at least one other expansion card contains the value 1 in
the current bit of its serial identifier, and thus has driven the data
values 0.times.55 and 0.times.AA onto the data bus SD[7:0] in the first
and second I/O read cycles, respectively. Therefore, the expansion card(s)
that contain the value 0 in the current bit of its serial identifier
"loses out" in the current iteration of card isolation process. These
cards are put into the SLEEP state in step 216, and will participate only
in future iterations of the isolation process. The expansion cards that
are placed into the SLEEP state in step 216 are not activated until the
command WAKE[0] is asserted again.
In step 212, if it is determined that the data bus SD[1:0] is not equal to
the binary value 10, which indicates that no other expansion card is
driving the value 0.times.AA onto the data bus SD[7:0], then control
proceeds to step 214. In step 214 it is determined if all 72 bits of the
serial identifier have been read. If not, control proceeds from step 214
to step 218, where the next serial identifier bit in each of the expansion
cards is fetched. Control proceeds from step 218 back to step 202, where
the isolation process is repeated. If in step 214, it is determined that
all 72 bits of the serial identifier has been read, which indicates that
an expansion card has been isolated, control then returns back to the
configuration routine. At this time, only one expansion card should still
be active as CSN[0]. All other expansion cards will be in sleep state or
will have a different CSN value.
Returning now to FIG. 1, control proceeds from step 106 to step 108, where
the isolated expansion card is assigned a unique handle, which is also
referred to as the card select number (CSN). The CSN is later used to
select the expansion card. Expansion cards that have been assigned a
non-zero CSN value will not participate in subsequent iterations of the
isolation process in step 106. Once an expansion card is assigned a
non-zero CSN value, it can respond to other bus commands. After the CSN is
assigned for the expansion card, control proceeds from step 108 to 110,
where the system BIOS performs resource data read cycles on the isolated
expansion card. The resource data describes all the resource requirements
of the Plug and Play ISA expansion card. The resource data includes such
items as the Plug and Play version number, the number of logical devices
(that is, the number of functions available on the Plug and Play expansion
card), the logical device ID, compatible device ID, IRQ format, DMA
format, I/O port descriptor, fixed location I/O port descriptor, memory
range descriptor, identifier string and various other information. The
resource data, along with the serial identifier described earlier in step
106, are conventionally stored in a serial EEPROM, which is typically 2K
bits in size. The expansion card resource data is initially read into a
resource data register located on the expansion card. After 8 bits have
been loaded into the resource data register, a status flag on the
expansion card is set indicating that the next byte of resource data is
ready to be outputted. Thus, the system BIOS will read the resource data
one byte at a time from the resource data register. This process is
repeated until all the resource data has been read, in which case, control
proceeds to step 112, where it is determined if all the Plug and Play
expansion cards have been accessed. If not, control returns to step 104,
where the configuration routine is reiterated. If all the cards have been
accessed, then control proceeds to step 114.
In step 114, the system resources are assigned to each expansion card. For
those expansion cards with more than one logical device, each logical
device is assigned resources separately. Configuration registers are
located on each expansion card for configuring the card's standard ISA
resource usage for each logical device. To program the configuration
registers, the system BIOS sends a command WAKE[CSN], along with write
data to set the desired CSN. The selected expansion card enters into a
CONFIG state, and all other expansion cards are forced into a SLEEP state.
Next, a logical device number is written to the logical device number
register to select the device that is to be programmed. After the proper
logical device is selected, the configuration registers are written with
the proper configuration values. Thus, memory configuration, I/O space
configuration, interrupt request level configuration and DMA channel
configuration are performed for each logical device. After the system
resources for a logical device are assigned, the logical device is
activated on the ISA bus. After all the configuration registers on an
expansion card are programmed, the expansion card is placed into the WAIT
FOR KEY state. Thus, if it is desired at a later time to access the Plug
and Play configuration registers, the initiation key can be issued by the
system BIOS to access the desired expansion card. It is noted that the
Plug and Play registers can be reprogrammed even in the operating system
environment. This is desirable for docking stations, as well as for
computer systems that support hot insertion capability and power
management. After all the expansion cards have been configured and all the
logical devices have been activated, the system BIOS exits the Plug and
Play configuration routine, and the standard POST procedure is executed.
The preceding describes the general steps in which Plug and Play ISA
expansion cards are configured. Depending upon the type of computer
system, the configuration algorithm may be different. For a more complete
description of Plug and Play ISA systems, refer to Plug and Play ISA
Specification (1994), Intel Corporation and Microsoft Corporation; and
Plug and Play BIOS Specification (1993), Compaq Computer Corporation,
Phoenix Technologies Ltd. and Intel Corporation. Both specifications are
hereby incorporated by reference.
Generally, when the Plug and Play expansion cards are connected to the ISA
bus, the serial EEPROM for storage of the serial identifier and Plug and
Play resource data is required. However, in certain cases, the functions
and logic of the expansion card may be located on the system board of the
computer. In this location, the system BIOS, which is specific to the
system board, will know that the functions are present. However, for full
compatibility with Plug and Play, a serial EEPROM will still be required
to conform to the Plug and Play protocol. This serial EEPROM adds cost to
the system and appears unnecessary as the system BIOS or other storage
device could readily contain the serial identifier and resource data
needed for Plug and Play compatibility. But the serial EEPROM has
nonetheless been considered necessary for Plug and Play compatibility,
increasing system cost. Removal of the serial EEPROM is thus desirable
while retaining Plug and Play compatibility.
SUMMARY OF THE PRESENT INVENTION
According to the present invention, an apparatus and method is developed
that avoids the need for a separate configuration storage device for Plug
and Play expansion cards. The apparatus includes the standard Plug and
Play capabilities to allow for standard Plug and Play configuration.
However, an indicating means is provided as part of the apparatus to allow
for an alternative configuration method. In the preferred embodiment of
the present invention, two embodiments of two alternative configuration
modes are provided. In both alternative modes of the first embodiment, the
standard Plug and Play isolation process is initially ignored and the
expansion cards do not receive card select numbers (CSN). In the first
alternative configuration mode, a dedicated register is mapped to a fixed
ISA I/O address. This register is used to enable or disable the standard
Plug and Play configuration registers on the expansion card. Thus the
configuration data for the expansion card can be written under system CPU
control to the configuration registers. In the second alternative
configuration mode in the first embodiment, a pin on the expansion card is
used as a chip select input for the dedicated register. In this second
mode, the register is not mapped to a fixed address, but may be mapped to
any location by other system board hardware.
In the second embodiment, the dedicated register is selected in the same
manner as the first embodiment, but instead of directly loading the
configuration data, the serial identifier and resource data are loaded
into a small RAM area when the dedicated register is enabled. When the
dedicated register is disabled, this small RAM area is used to provide the
serial identifier and configuration data to the Plug and Play logic
instead of the serial EEPROM. This second embodiment allows configuration
according to full Plug and Play convention, while the first embodiment has
the expansion functions determined and written outside of the Plug and
Play software.
Preferably, pullup and pulldown resistors are used to indicate whether the
standard Plug and Play configuration mode or one of the alternative
configuration modes is utilized by the expansion card.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention can be obtained when the
following detailed description of the preferred embodiment is considered
in conjunction with the following drawings, in which:
FIG. 1 is a flowchart of the Plug and Play isolation and configuration
process;
FIG. 2 is a flowchart of the output driving logic of a Plug and Play device
during isolation;
FIG. 3 is an exemplary computer system incorporating the preferred
embodiment of the present invention;
FIG. 4 is a block diagram of a Plug and Play device according to the
present invention;
FIG. 5 shows a portion of the device of FIG. 4 that supports the
configuration of the device;
FIG. 6 is a schematic diagram of the initiation key recognition logic;
FIG. 7 is a state diagram of the state machine for placing the device of
FIG. 4 in the appropriate state;
FIG. 8 shows the logic for determining whether the device of FIG. 4 has
"lost out" in the current isolation process;
FIGS. 9A and 9B are a schematic diagram of the EEPROM interface;
FIG. 10 is a state diagram of the state machine that reads data from the
serial EEPROM;
FIG. 11 is a schematic diagram of the output port of the device of FIG. 4;
and
FIG. 12 is a schematic diagram of logic for receiving the serial identifier
and resource data into a RAM.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 3, a computer system S incorporating a device
according to the present invention is shown. The computer system S
includes a host CPU or processor 300, which is conventionally a
microprocessor such as a 486 or Pentium from Intel Corporation. A host bus
302 is connected to the CPU 300 to act as a first bus in the computer
system S. A cache unit 304 is connected to the host bus 302 to cache
memory operations of the CPU 300. A main memory system 306 is also
connected to the host bus 302 to act as the main memory of the computer
system S. A video system 308 is further connected to the host bus 302 to
allow high performance operation of the video system 308.
A bus controller 310 is connected between the host bus 302 and an ISA or
Industry Standard Architecture bus 312. A system peripheral 314 is
connected to the bus controller 310 and the ISA bus 312. The system
peripheral 314 includes certain common peripheral devices used in the
computer system S such as timers, an interrupt controller and, of
importance to this particular application, a DMA controller as
conventional in IBM PC compatible computers. A number of ISA slots 316 for
receiving interchangeable circuit cards are present on the ISA bus 312. In
a conventional embodiment an audio/modem card 318 according to the Plug
and Play specification would be located in one of the ISA slots 316. In
the preferred embodiment, the audio/modem card 318 is directly mounted
onto the system board and connected directly to the ISA bus 312, or
alternatively to the X bus 322. When directly mounted, the audio/modem
card 318 would be considered as a system board device rather than an
expansion device. When the audio/modem card 318 is connected to the ISA
slots 316, a separate serial EEPROM 330 conventionally is required to
store the audio/modem card's configuration data. In accordance with the
Plug and Play specification, the audio/modem card 318 requires no
configuration switches or jumpers. In accordance with the present
invention, no separate configuration ROM is required when the audio/modem
card 318 is directly mounted on the system board. The configuration data
for the audio/modem card 318 is stored in another storage device available
in the computer system, such as the system BIOS ROM 324 or on the system
hard disk drive.
Appropriate buffer and transceiver logic 320 is connected between the ISA
bus 312 and an X bus 322, which forms an additional input/output (I/O) bus
in the computer system S. A read only memory or ROM 324, which contains
the instructions forming the BIOS and other fundamental operations, is
connected to the X bus 322. A keyboard controller 326 is connected to the
X bus 322 to receive keyboard and pointing device inputs from a user.
Parallel and serial 328 ports as are conventional are connected to the X
bus 322 to provide certain I/O capabilities. A hard disk interface 323 is
connected to the X bus 322 to allow use of a hard disk drive.
FIG. 3 illustrates an exemplary computer system and it is understood that
other conventional computer systems having different architectures could
be utilized and that the computer system S of FIG. 3 has been shown only
for a representative embodiment to place the preferred embodiment of the
invention in context. It is also understood that the audio/modem card 318
is merely an exemplary Plug and Play expansion card, and that other Plug
and Play cards can incorporate the present invention.
Referring now to FIG. 4, the audio/modem card 318 is shown in more detail.
An interface application specific integrated circuit (ASIC) 350 forms the
core of the audio/modem card 318. A DSP bus 352 is provided from the
interface ASIC 350 and is connected to a DSP or digital signal processing
computer 354, static random access memory or SRAM 356 which is utilized by
the DSP 354 and, in the preferred embodiment, a wavetable ROM 358. The
wavetable ROM 358 contains certain wavetable information used in audio
output situations. The DSP 354 is preferably one of the many high
performance DSPs available and, in the preferred embodiment, is the
Motorola 56002. This DSP 354 is a 24-bit unit and can access 64K words of
memory in several different address spaces. The interface ASIC 350 is
further connected to an audio codec 360 referred to as the PBIC.
Preferably the audio codec 360 is the AD1848 device made by Analog
Devices. The DSP 354 is connected to a wavetable DAC or digital to analog
converter 362. The wavetable DAC 362 takes the wavetable data from a
wavetable ROM 358, as processed by the DSP 354, and converts it to an
analog audio signal. The outputs of the audio codec 360 and the wavetable
DAC 362 are provided to an analog audio chip 364, which contains
amplifiers and mixing circuits. The analog audio chip 364 includes a
microphone input, a speaker output and left and right line level inputs
and outputs as conventional in audio systems.
The interface ASIC 350 includes a block referred to as the Plug and Play
logic 351. The Plug and Play logic 351 provides the necessary logic to
allow switchless configuration of the audio/modem card 318. The Plug and
Play logic 351 is connected to the serial EEPROM 330 if utilized in
separate card mode to fully conform with the Plug and Play specification.
In the preferred embodiments, the Plug and Play logic 351 also
incorporates circuitry for use when a serial EEPROM 330 is not provided.
The Plug and Play logic 351 is generally shown in the remaining figures
and described below.
The interface ASIC 350 is connected to two pullup or pulldown resistors 380
and 382 through specified output pins. The resistors 380 and 382 are
either tied high or low, depending upon which configuration mode is being
utilized. When both resistors 380 and 382 are tied low, the standard Plug
and Play configuration mode is selected. If the resistor 380 is tied high
and the resistor 382 is pulled low, the first alternative configuration
mode is chosen. If the resistor 380 is pulled low and the resistor 382 is
tied high, the second alternative configuration mode is selected. The
resistors 380 and 382 are preferably connected to output pins HA[0:1],
respectively, on the audio/modem card 318. The pins HA[0:1] are the two
least significant DSP host interface address bus pins, which are used to
select the register address in the DSP's host interface during accesses to
those registers. The pins HA[0:1] are tristated during power up reset to
allow the states defined by the resistors 380 and 382 to be detected.
This state determination is shown in FIG. 5. The signal HA[1] is provided
to the D input of a D-type latch 380. The latch is gated by the signal
RST*, the reset signal in the computer system S. The signal HA[0] is
provided to the D input of a D-type latch 382, which is also gated by the
signal RST*. The noninverted output of the latch 382 and the inverted
output of the latch 380 are two inputs to an AND gate 384, whose output is
the signal MODE.sub.-- 1 or first mode signal. The third input to the AND
gate 384 is the signal RST*. The non-inverted output of the latch 380, the
inverted output of the latch 382 and the signal RST* are the inputs of an
AND gate 386, whose output is the signal MODE.sub.-- 2 or second mode
signal. The signals MODE.sub.-- 1 and MODE.sub.-- 2 are provided to an OR
gate 388 to develop a signal MODE.sub.-- 1.sub.-- OR.sub.-- 2.
A modem daughterboard 366 is connected to the interface ASIC 350 over a bus
368 having serial and parallel data transfer portions. A modem codec 370
is located on the daughterboard 366 and receives the bus 368 from the
interface ASIC 350. A data access arrangement or DAA 372 is connected to
the modem codec 370 and the interface ASIC 350. A telephone jack 374 is
connected to the DAA 372 to provide an interface to the telephone system.
Alternatively, the daughterboard 366 could contain other standard
telephony interfaces, such as ISDN, or a high speed serial link for PBX or
general purpose applications. The provision of the daughterboard 366 in
conjunction with the DSP 354 allows low cost addition of modem functions,
as indicated in copending application Ser. No. 08/094,491, entitled
"Apparatus for Adding Modem Capabilities to a Computer System Equipped
with a Digital Signal Processor," filed Jul. 19, 1993, and its
continuation application Ser. No. 08/404,942, filed Mar. 15, 1995,
pending, each of which is hereby incorporated by reference.
Referring again to FIG. 5, portions of the Plug and Play logic 351 are
shown. The audio/modem card 318 includes three Plug and Play ports; an
ADDRESS port, a WRITE.sub.-- DATA port and a READ.sub.-- DATA port. The
ADDRESS and WRITE.sub.-- DATA ports are located at predetermined ISA
addresses, while the READ.sub.-- DATA port is programmable between a range
of ISA addresses. The address provided to an address port is latched into
a register 400 on the falling edge of a strobe WRT.sub.-- ADDR.sub.--
STRB. The signal WRT.sub.-- ADDR.sub.-- STRB is asserted high when the
address port is accessed with the proper ISA address, the ISA write strobe
IOWC* is asserted low, and the audio/modem card 318 is not in a WAIT FOR
KEY state or a signal ALT.sub.-- CSN.sub.-- SEL is asserted high. As
described above, the WAIT FOR KEY state is a state in which a Plug and
Play expansion card waits for an initiation key, ignoring all other
accesses. The signal ALT.sub.-- CSN.sub.-- SEL is asserted when the
audio/modem card 318 board is in one of two alternative configuration
modes. In the first embodiment, when the signal ALT.sub.-- CSN.sub.-- SEL
is asserted high, the ISA isolation process is ignored and the audio/modem
card 318 does not receive a card select number (CSN) as required in a
standard Plug and Play configuration. Instead, in the first alternative
configuration mode, an alternative configuration register 402 on the
audio/modem card 318 is assigned to a fixed ISA I/O address. In the first
mode, all configuration information is written under the system CPU
control through the standard Plug and Play configuration registers. In a
second alternative configuration mode, a configuration select pin on the
interface ASIC 350 is used as an active low chip select input for an
alternative configuration register 402. Thus, in the second alternative
configuration mode the register 402 is not assigned to the predefined ISA
address in the first mode, but the register 402 can be mapped to any
location by the system board hardware. A second embodiment using the
signal ALT.sub.-- CSN.sub.-- SEL to enable the configuration is described
below in conjunction with FIG. 12.
The alternative configuration register 402 is clocked by the output of an
OR gate 404. The inputs of the OR gate 404 are connected to signals
ISA.sub.-- WR* and ISA.sub.-- ALTC.sub.-- CS*. The signal ISA.sub.-- WR*
is a general write strobe provided by other logic on the interface ASIC
350. The signal ISA.sub.-- ALTC.sub.-- CS* is asserted high if the
audio/modem card 318 is in the first configuration mode and the proper
predefined ISA address is asserted or if the card 318 is in the second
configuration mode, the configuration select pin is driven low. The D
input of the register 402 is connected to a signal DATIN[0], which is the
least significant bit of the data bus that is multiplexed between the SRAM
bus 352 and the ISA bus 312. The output of the D flip-flop 402 is the
ALT.sub.-- CSN.sub.-- SEL signal and is connected to an input of an OR
gate 406. The other input of the OR gate 406 is connected to a signal
CONFIG.sub.-- ST, which when asserted high indicates that the audio/modem
card 318 is in the CONFIG mode. The output of the OR gate 406 is connected
to the select input of a multiplexor 408. The multiplexor 408 provides
data to be latched into configuration registers, which are represented by
a block 410. The configuration registers 410 are loaded on the falling
edge of a signal WRT.sub.-- WRITE.sub.-- PORT, which is asserted when the
WRITE.sub.-- DATA port is accessed, the ISA write strobe IOWC* is asserted
low, and the card 318 is not in a WAIT FOR KEY state or the signal
ALT.sub.-- CSN.sub.-- SEL is asserted high. As there are a number of
logical devices on the audio/modem card 318, independent configuration
registers must be dedicated to each logical device. Signals LDN[7:0] are
provided to identify the appropriate set of configuration registers 410.
In the preferred embodiment, the audio/modem card 318 is divided into 8
logical devices. The actual configuration register of the particular
logical device is provided by the value in the address register 400. When
the select input of the multiplexor 408 is asserted high, data is provided
to the configuration registers 410 through the ISA data bus SD[7:0].
Otherwise the outputs of the configuration registers 410 are provided to
their inputs through the I0 input of the multiplexor 408, and the state of
the configuration registers 410 is not changed. The configuration
registers 410 are reset to their initial conditions on the falling edge of
a signal LOG.sub.-- RST*, which is asserted low when the system reset
signal RST* is low or bit 0 of a configuration control register 430 is
written with a 1.
Therefore the use of the alternate configuration modes and the ALT.sub.--
CSN.sub.-- SEL signal allows bypassing of the Plug and Play configuration
process as the configuration registers can be accessed without requiring
isolation and configuration according to the Plug and Play specification.
This is acceptable as the system BIOS knows that the audio/modem card 318
is present and can include its resource requirements in any configuration
process, these resource requirements being stored in the system BIOS or
other device such as the hard disk drive. With this process the serial
EEPROM 330 is not required for configuration of the audio/modem card 318
when it is installed on the system board.
The 3-bit register 430 stores three configuration control bits. The output
of the register 430 is represented by signals CFG.sub.-- DATA[2:0]. A
write to bit 0 of the configuration control register 430 performs a reset
of all the logical devices on the audio/modem card 318, as well as the
contents of the configuration registers 410 1 CLK cycle later. A write to
bit 1 of the configuration control register 430 causes the audio/modem
card 318 to enter the WAIT FOR KEY state. A write to the second bit of the
register 430 causes the audio/modem card 318 to reset CSN to 0. The input
of the register 430 is connected to the output of a 3 bit, two input
multiplexor 432. The I0 input of the multiplexor 432 is connected to the
signals CFG.sub.-- DATA[2:0], and the I1 input is connected to the data
bus SD[2:0]. The select input of the multiplexor 432 is connected to a
signal ADR.sub.-- CFG, which is asserted high when the contents of the
address register 400 contains an address port value corresponding to the
configuration control register 430. The register 430 is clocked on the
falling edge of a signal WRT.sub.-- WRITE.sub.-- PORT and is reset by the
falling edge of a signal CFG.sub.-- RST*. The signal CFG.sub.-- RST* is
asserted low if the system reset signal RST* is asserted. The signal
CFG.sub.-- RST* is also asserted low two clock cycles after the
configuration control register 430 is written.
The ISA address for the READ.sub.-- DATA port is stored in a register 412.
The register 412 is clocked by the falling edge of the signal WRT.sub.--
WRITE.sub.-- PORT and is reset by the falling edge of a signal RST*. The D
input of the register 412 is connected to the output of an eight bit, two
input multiplexor 414. The I0 input of the multiplexor 414 is connected to
the output of the register 412, which is represented by signals RD.sub.--
PORT[7:0]. The I1 input of the multiplexor 414 is connected to the data
bus SD[7:0], and its select input is connected to a signal ADR.sub.--
RD.sub.-- DAT, which is asserted high when the address register 400
contains an address port value corresponding to the read port register
412.
Also located in the interface ASIC 350 is a latch 418, whose data input is
connected to the output of a multiplexor 422. Data from the multiplexor
422 is latched whenever the output of an OR gate 420 or the data bus
SD[7:0] change state. The inputs of the OR gate 420 are connected to a
signal ADR.sub.-- WAKE and the signal WRT.sub.-- WRITE.sub.-- PORT. The
signal ADR.sub.-- WAKE is asserted high when the address register contains
an address port value corresponding to the latch 418. The output of the
latch 418 provides signals WAKE.sub.-- DAT[7:0]. The input to the latch
418 is provided by the data bus SD[7:0]. Data is latched into the latch
418 from the data bus SD[7:0] whenever a write to the write port occurs
with the address equal to the wake value. A write to the wake data latch
418 causes the audio/modem card 318 to go from the SLEEP state to the
ISOLATION state if the data written into the latch 418 is 0 or the CONFIG
state if the data written is not 0.
Another register located in the interface ASIC 350 is the CSN register 424.
The register 424 is clocked by the falling edge of the signal WRT.sub.--
WRITE.sub.-- PORT and is reset on the falling edge of a signal CSN.sub.--
RST*. The D input of the register 424 is connected to the output of a
multiplexor 428. The I0 input of the multiplexor 428 is connected to the
output of the register 424, which is represented by signals CSN[7:0]. The
I1 input of the multiplexor 428 is connected to the data bus SD[7:0], and
its select input is connected to the output of an AND gate 426. The inputs
of the AND gate 426 are connected to a signal ISO.sub.-- ST and a signal
ADR.sub.-- CSN. When asserted high, the signal ISO.sub.-- ST indicates
that the audio/modem card 318 is in the ISOLATION state. The signal
ADR.sub.-- CSN is asserted high when the address register 400 contains a
value corresponding to the CSN register 424. The signal CSN.sub.-- RST* is
asserted low when the system reset signal RST* is asserted or if bit 2 of
the configuration control register 430 is written with the value 1.
The signals LDN[7:0] are provided by a logical device number register 440.
The register 440 is clocked on the falling edge of the signal WRT.sub.--
WRITE.sub.-- PORT and is reset on the falling edge of the system reset
signal RST*. The D input of the register 440 is connected to the output of
a multiplexor 442. The I0 input of the multiplexor 442 is connected to the
signals LDN[7:0], and its I1 input is connected to the data bus SD[7:0].
The select input of the multiplexor 442 is connected to the output of an
AND gate 444, whose inputs are connected to the output of an OR gate 446
and to the signal ADR.sub.-- LOGDEV. The inputs of the 0R gate 446 are
connected to the signal CONFIG.sub.-- ST and the signal ALT.sub.--
CSN.sub.-- SEL. The signal ADR.sub.-- LOGDEV is asserted high when the
contents of the address register 400 contains an address port value
corresponding to the logical device number register 440. Thus, if the
audio/modem card 318 is in the configuration state or if an alternative
configuration mode is selected, the AND gate 444 outputs a high to the
select input of the multiplexor 442. As a result, the contents of the data
bus SD[7:0] is latched into the register 440 on the rising edge of the
signal WRT.sub.-- WRITE.sub.-- PORT.
Referring now to FIG. 6, a circuit is shown that determines whether an
initiation key has been provided by the system BIOS. It is assumed that
the audio/modem card 318 is set to the standard Plug and Play
configuration mode in the ensuing description. The audio/modem card 318
uses a linear feedback shift register (LFSR) to generate data patterns
needed to provide an initiation key protocol. The LFSR is built with D
flip-flops 500-507, which are clocked by the signal LFSR STRB. The outputs
of the D flip-flops 500-507 correspond to signals LFSR[0:7], respectively.
On the rising edge of the signal LFSR.sub.-- STRB, a shift operation is
performed, in which the signal LFSR[7] is latched into the D flip-flop
506, the signal LFSR[6] is latched into the D flip-flop 505, the signal
LFSR[5] is latched into the D flip-flop 504, the signal LFSR[4] is latched
into the D flip-flop 503, the signal LFSR[3] is latched into the D
flip-flop 502, the signal LFSR[2] is latched into the D flip-flop 501, the
signal LFSR[1] is latched into the D flip-flop 500, and the output of an
XOR gate 510 is latched into D flip-flop 507. The inputs of the XOR gate
510 are connected to the signals LFSR[1] and LFSR[0]. The D flip-flops
500-507 are reset to the value 0.times.6A on the falling edge of the
output of an AND gate 512. The inputs of the AND gate 512 are connected to
the system reset signal RST*, the inverted state of a signal WAIT.sub.--
CMD and a signal LFSR.sub.-- NEQ*. The signal WAIT.sub.-- CMD is asserted
low one clock cycle after bit 1 of the configuration control register 430
is written with the value 1. In the preferred embodiment, the clock signal
used is CLK, which is the DSP clock signal. The signal LFSR.sub.-- STRB is
provided by a D flip-flop 514 and the signal LFSR.sub.-- NEQ* is provided
by a D flip-flop 516. Both the D flip-flops 514 and 516 are clocked on the
falling edge of a signal WRT.sub.-- LFSR.sub.-- STRB, which is asserted
when the ADDRESS port and the WRITE.sub.-- DATA port of the audio/modem
card 318 are accessed and the ISA write signal IOWC* is asserted low. The
D flip-flops 514 and 516 are reset on the falling edge of a signal
STRB.sub.-- RST*. The signal STRB.sub. -- RST* is asserted low when the
system reset signal RST* is asserted or during the clock cycle after the
signal WRT.sub.-- LFSR.sub.-- STRB is asserted. A write to the WRT.sub.--
DATA port, represented by a signal WRSTB being asserted high, causes the
contents of the data bus SD[7:0] to be loaded into a data register 520.
The data register 520 is gated by the signal WRSTB, which is asserted
during the write cycle to the WRT.sub.-- DATA port. The output signals
SD.sub.-- LATCH[7:0] of the data register 520 are compared by a comparator
522 to the signals LFSR[7:0] provided by the D flip-flops 500-507. If a
match occurs, the comparator 522 outputs 1's to the D inputs of the D
flip-flops 514 and 516. As a result, on the falling edge of the signal
WRT.sub.-- LFSR.sub.-- STRB, the signals LFSR.sub.-- STRB and LFSR.sub.--
NEQ* are both set high. When the signal LFSR.sub.-- STRB transitions high,
the contents of the D flip-flops 500-507 are shifted in the manner
described above. If the value of the signals SD.sub.-- LATCH[7:0 ] do not
match the value of the signals LFSR.sub.-- [7:0], the comparator 522
outputs a low state, which causes the signals LFSR.sub.-- STRB and
LFSR.sub.-- NEQ* to both be set low. When the signal LFSR.sub.-- NEQ* is
set low, the D flip-flops 500-507 are initialized to the initial state of
0.times.6A. A non-match by the comparator 522 signifies that an improper
initiation key has been written to the WRT.sub.-- DATA port. The output of
the comparator 522 is also provided to an input of an AND gate 524. The
other input of the AND gate 524 is connected to the output of a comparator
526, which compares the values of the signals SD.sub.-- LATCH[7:0] to the
value 0.times.39. Thus, if the value of signals LFSR[7:0] is equal to the
value 0.times.39, and the value of the signals SD.sub.-- LATCH[7:0] is
equal to the signals LFSR[7:0], then the comparators 522 and 526 drive
their respective outputs high. In this case, the output of the AND gate
524, which is connected to the D input of a D flip-flop 518, is driven
high. The D flip-flop 518 is clocked by the signal WRT.sub.-- LFSR.sub.--
STRB and reset by the signal STRB.sub.-- RST*. The output of the D
flip-flop 518 is connected to a signal KEY.sub.-- GOOD. Thus, a match by
the comparators 522 and 526 causes the signal KEY.sub.-- GOOD to be
asserted high. The signal KEY.sub.-- GOOD indicates that the proper
initiation key has been written to the WRT.sub.-- DATA port. In operation,
the exact sequence for the initiation key is as follows: 0.times.6A,
0.times.B5, 0.times.DA, 0.times.ED, 0.times.F6, 0.times.FB, 0.times.7D,
0.times.BE, 0.times.DF, 0.times.6F, 0.times.37, 0.times.1B, 0.times.0D,
0.times.86, 0.times.C3, 0.times.61, 0.times.B0, 0.times.58, 0.times.2C,
0.times.16, 0.times.8B, 0.times.45, 0.times.A2, 0.times.D1, 0.times.E8,
0.times.74, 0.times.3A, 0.times.9D, 0.times.CE, 0.times.E7, 0.times.73 and
0.times.39. If the preceding sequence of data is properly provided to the
WRT.sub.-- DATA port of the audio/modem card 318, the signal KEY.sub.--
GOOD is set high when the last value 0.times.39 is received. Any deviation
from the exact sequence would cause the D flip-flops 500-507 to be reset
to the initial value of 0.times.6A.
Referring now to FIG. 7, a state diagram is shown of a state machine
located in the interface ASIC 350 that determines the state of the
expansion card. On the falling edge of the system reset signal RST*, the
state machine enters into a WAIT FOR KEY state. In response to the reset
signal RST* being asserted low, the CSN is reset to the value zero. The
WAIT FOR KEY state is represented by a signal WAIT.sub.-- ST being
asserted high. If the proper initiation key is provided to the expansion
card, the signal KEY.sub.-- GOOD is asserted high, causing the state
machine to transition from the WAIT FOR KEY state to the SLEEP state,
which is represented by a signal SLEEP.sub.-- ST being asserted high. Once
the state machine enters into the SLEEP state, the signal WAIT.sub.-- CMD
asserted high causes the state machine to transition from the SLEEP state
back to the WAIT FOR KEY state. The signal WAIT.sub.-- CMD represents the
WAIT FOR KEY command, and is asserted high when a 1 is written to bit 1 of
the configuration control register. From the SLEEP state, the state
machine transitions to the ISOLATION state when both signals WAKE.sub.--
EQ.sub.-- ZERO and CSN.sub.-- EQ.sub.-- ZERO are high. The signal
CSN.sub.-- EQ.sub.-- ZERO is asserted high when the CSN register 424
contains the value 0. The signal WAKE.sub.-- EQ.sub.-- ZERO is asserted
high when the wake data latch 418 is written with a value 0. The ISOLATION
state is represented by a signal ISO.sub.-- ST being asserted high. Once
the expansion cards are placed into the ISOLATION state, an isolation
process is run by the system BIOS to isolate the expansion cards inserted
into the ISA slots 316, so that a chip select number (CSN) can be assigned
to each individual expansion card. The logic on the expansion cards that
are involved in the isolation routine is shown in FIG. 8, which will be
described in greater detail. If the WAIT FOR KEY command WAIT.sub.-- CMD
is issued when the state machine is in the ISOLATION state, control
returns to the WAIT FOR KEY state. Otherwise, each expansion card stays in
the isolation state until one of the expansion cards is isolated by the
isolation process. Once an expansion card has been isolated, it is
assigned a unique CSN by writing the CSN register 424. A write to the CSN
register 424 causes a signal CSN.sub.-- SET to be asserted high, which in
turn causes the state machine on the isolated expansion card to transition
from the ISOLATION state to the CONFIG state. However, on the expansion
cards that have "lost out" during the isolation routine, a signal
LOSE.sub.-- ISO is asserted. This causes the state machine on those
expansion cards to transition from the ISOLATION state back to the SLEEP
state. The expansion cards that are placed into the SLEEP state withdraw
from further participation in the current isolation process.
Once an expansion card is isolated and assigned a CSN value, it transitions
to the CONFIG state. In the CONFIG state, the expansion card is responsive
to a resource data read cycle. The resource data read cycle is decoded
when the ADDRESS port and the READ.sub.-- DATA port are accessed and the
ISA read command strobe IORC* is issued. The ADDRESS port must be written
with the proper address port value. Once all the resource data has been
read from the expansion card, the system BIOS issues a WAKE command,
writing the wake data latch 418 with the value zero to send the state
machine back to a SLEEP state.
The state machine can also transition from the ISOLATION state to the SLEEP
state when a signal WAKE.sub.-- NEQ.sub.-- CSN is asserted high, which
occurs when the wake data register 418 is written with a value that is not
equal to CSN. The signal WAKE.sub.-- NEQ.sub.-- CSN being asserted high
also causes the state machine to transition from the CONFIG state back to
the SLEEP state. It is noted that if the CSN value is set equal to 0, the
signal WAKE.sub.-- NEQ.sub.-- CSN would be equivalent to the inverted
state of the signal WAKE.sub.-- EQ.sub.-- ZERO. When that occurs, the
expansion card that has been assigned the non-zero CSN value transitions
from the CONFIG state back to the SLEEP state while all the expansion
cards that were in the SLEEP state as a result of "losing out" during the
isolation process transition from the SLEEP state to the ISOLATION state.
As a result, the expansion card that has been assigned a unique CSN value
is kept in the SLEEP state while the remaining expansion cards are
subjected to the isolation process. The isolation process is repeated
until all Plug and Play expansion cards connected to the ISA slots 316 are
assigned unique CSN values. The expansion cards with assigned non-zero
CSN's would not respond to the signals WAKE.sub.-- EQ.sub.-- ZERO and
CSN.sub.-- EQ.sub.-- ZERO being asserted high. Once all the expansion
cards have been assigned a CSN value, they all end up ultimately in the
SLEEP state. The expansion cards stay in the SLEEP state until a signal
WAKE.sub.-- EQ.sub.-- CSN is asserted high and the signal WAKE.sub.--
EQ.sub.-- ZERO is deasserted low. The signal WAKE.sub.-- EQ.sub.-- CSN is
asserted high when the wake data register 418 is written with a value
equal to CSN[7:0]. When the signals WAKE.sub.-- EQ.sub.-- CSN and
WAKE.sub.-- EQ.sub.-- ZERO are asserted high and low, respectively, the
expansion card with the matching CSN value transitions from the SLEEP
state to the CONFIG state, where configuration registers on the expansion
card is programmed with the appropriate data. From the CONFIG state,
control can return back to the WAIT FOR KEY state upon issuance of the
WAIT FOR KEY command, which causes the signal WAIT.sub.-- CMD to be
asserted. It is also noted that the state machine transitions to the WAIT
FOR KEY state from any state upon assertion of the system reset signal
RST*.
Referring now to FIG. 8, logic on the audio/modem card 318 responsive to
the isolation process executed by the system BIOS is shown. Three D
flip-flops 700, 702 and 704 provide signals ISO.sub.-- 55, LOSE.sub.-- ISO
and ISO.sub.-- CYCLE, respectively. The signal ISO.sub.-- 55, when set
high, indicates that the data bus SD[7:0] is being driven with the value
0.times.55. The signal LOSE.sub.-- ISO being set high indicates that the
audio/modem card 318 has "lost out" in the current isolation process. The
signal ISO.sub.-- CYCLE indicates the phase of the serial isolation
register read cycle. As described in FIG. 2, a pair of reads are performed
for each bit of the serial isolation register. Thus, if the signal
ISO.sub.-- CYCLE is low, that indicates the first read is being performed.
If the signal ISO.sub.-- CYCLE is asserted high, then that indicates the
second read of the same serial isolation register bit is being performed.
The three D flip-flops 700-704 are clocked on the rising edge of the clock
signal CLK, and are reset on the falling edge of the output of an AND gate
706. The first input of the AND gate 706 is tied to the system reset
signal RST*, and the second input is tied to the inverted state of the
signal SLEEP.sub.-- ST, which indicates that the audio/modem card 318 is
in the SLEEP state. Thus if the reset signal RST* is asserted low or the
signal SLEEP.sub.-- ST is asserted high, then the D flip-flops 700, 702
and 704 would all be reset low. The D inputs of the D flip-flops 700, 702
and 704 are connected to the outputs of multiplexors 708, 710 and 712,
respectively. The S1 input of the multiplexor 708 is connected to the
output of an AND gate 726, and its SO input is connected to the output of
an AND gate 716. The I0 input of the multiplexor 708 is connected to the
signal ISO.sub.-- 55, the I1 input is tied high, and the I2 input is tied
low. The S1 input of the multiplexor 710 is connected to the output of the
AND gate 714 and its S0 input is tied to the output of an AND gate 718.
The I0 input of the multiplexor 710 is connected to the signal LOSE.sub.--
ISO, the I1 input is tied low, and the I2 input is tied high. For the
multiplexor 712, the S1 input is tied to the output of the AND gate 726,
and the SO input is tied to the output of an AND gate 720. The I0 input of
the multiplexor 712 is connected to the signal ISO.sub.-- CYCLE, the I1
input is tied high, and the I2 input is tied low.
The inputs of the AND gate 714 are connected to the output of an AND gate
724 and the output of an AND gate 726. The inputs of the AND gate 724 are
connected to the signal ISO.sub.-- 55, the inverted state of a signal
ISOKEY and the output of a comparator 734. The comparator 734 compares the
value of the signals ISO.sub.-- SD[1:0], which is the latched values of
the data bus SD[1:0], with the value 0b10. A match indicated by the
comparator 734 signifies that the ISA data bus SD[7:0] is being driven
with the value 0.times.AA. The inputs of the AND gate 726 are connected to
the signal ISO.sub.-- CYCLE and the output of an AND gate 732, whose
inputs are connected to a signal RD.sub.-- ISO.sub.-- D and the inverted
state of a signal RD.sub.-- ISO. The signal RD.sub.-- ISO, when asserted
high, indicates that a read of the serial isolation register is occurring.
The signal RD.sub.-- ISO.sub.-- D is equivalent to the signal RD.sub.--
ISO delayed by one CLK cycle. The output of the AND gate 732 is connected
to the input of an inverter 728, whose output drives an input of the AND
gate 718. The other input of the AND gate 718 is connected to the signal
LOSE.sub.-- ISO. The output of the AND gate 732 is also connected to an
input of the AND gate 720, whose other input is connected to the inverted
state of the signal ISO.sub.-- CYCLE. The output of the AND gate 720 is
provided to an input of the AND gate 716. The other input of the AND gate
716 is connected to the output of an AND gate 722. The first input of the
AND gate 722 is connected to the inverted state of the signal ISOKEY, and
its second input is connected to the output of a comparator 730, which
compares the value of the signals ISO.sub.-- SD[1:0] with the value 0b01.
Thus, if the ISA data bus SD[7:0] is being driven with the value
0.times.55, the comparator 730 outputs a high state. The signal ISOKEY
represents the current bit read from the serial isolation register. During
the isolation process, the isolation register contains two bytes of the
expansion card serial identifier. If the current bit of the serial
identifier is a 0, which means that the signal ISOKEY is low, and the
value 0.times.55 is driven on the data bus SD[7:0] by at least one other
expansion card, the AND gate 722 drives its output high. As can be seen
from the logic, if the current bit of the serial identifier is high, then
the D flip-flops 700 and 702 are maintained in their off state. The only
signal that is allowed to change is the signal ISO.sub.-- CYCLE
corresponding to the D flip-flop 704. The reason for ignoring the states
of the signals ISO.sub.-- 55 and LOSE.sub.-- ISO, when the current serial
identifier bit is a 1, is that such an expansion card is actively driving
the data bus SD[7:0] with the values 0.times.55 and 0.times.AA in the
first and second read cycles, respectively. As a consequence, the
expansion card would not "lose out" in the current isolation process. When
the first read of the serial isolation register is being performed, the
signal ISO.sub.-- CYCLE is low, which causes the AND gate 720 to output a
high. As a result, the output of the AND gate 716 to also driven high.
Since the output of the AND gate 726 at this time is low, the I1 input of
the multiplexor 708 is selected, and its value provided to the D input of
the D flip-flop 700. As a result, the D flip-flop 700 is latched with the
value 1 on the rising edge of the CLK, thereby driving the signal
ISO.sub.-- 55 high. Because the signal LOSE.sub.-- ISO is initialized to
low, the AND gate 718 initially outputs a low. Since both the outputs of
the AND gate 714 and 718 are low at this time, the multiplexor 710 selects
its I0 input, which maintains the signal LOSE.sub.-- ISO at its current
state. Because the signal is initialized low, indicating that the first
read is performed, the output of the AND gate 720 is driven high, which
causes the multiplexor 712 to select its I1 input. As a result, a 1 is
loaded into the D flip-flop 704 to drive the signal ISO.sub.-- CYCLE high.
When this occurs, the AND gate 726 drives its output high. At the same
time, the expansion cards that were driving the value 0.times.55 onto the
data bus SD[7:0] now drive the value 0.times.AA. This causes the
comparator 734 to output a high state. Since the signal ISO.sub.-- 55 has
been set high and the signal ISOKEY, which represents the current bit of
the serial identifier, is low, the AND gate 724 drives its output high,
which causes the AND gate 714 to drive its output high, which in turn
causes each of the multiplexors 708, 710 and 712 to select its I2 input.
As a result, on the next rising edge of the signal CLK, the D flip-flop
700 sets the signal ISO.sub.-- 55 low, the D flip-flop 702 sets the signal
LOSE.sub.-- ISO high and the D flip-flop 704 sets the signal ISO.sub.--
CYCLE low.
Referring now to FIGS. 9A and 9B, a logic diagram is shown of the serial
EEPROM interface in the Plug and Play logic 351. A state machine 800 is
shown connected to the serial EEPROM 330. The state machine 800 provides a
signal SROM.sub.-- CS, which is the chip select signal, and a signal
SROM.sub.-- DI, which is connected to the serial input to the serial
EEPROM 330. The signal SROM.sub.-- CS is connected to the input of an
inverter 801. The output of the inverter 801 drives a signal SR.sub.--
OE*, which is connected to the output enable input of the serial EEPROM
330. The serial output of the serial EEPROM 330 is connected to the state
machine 800 via a signal SROM.sub.-- DO. A ROM address SROM.sub.--
ADDR[7:0] is provided to the state machine 800 that is representative of a
location in the serial EEPROM 330. The state machine 800 is clocked by a
signal SROM.sub.-- CLK*, an active low signal, whose frequency is
preferably 80 times less than the frequency of the signal CLK. The other
inputs to the state machine 800 are signals BITPTR[3:0], which is a
pointer to a bit in the serial isolation register located in the state
machine 800, and a signal FETCH16.sub.-- LAT, which indicates when
asserted to the state machine 800 that the next two bytes of data are to
be retrieved from the serial EEPROM 330. The other outputs of the state
machine 800 are a signal INC.sub.-- ADR, which indicates that the ROM
address SROM.sub.-- ADDR[7:0] is to be incremented, signals SROM.sub.--
DAT[15:0], which correspond to the outputs of the serial isolation
register, and a signal FETCH16.sub.-- CLR, which when asserted causes the
signal FETCH16.sub.-- LAT to be reset low. The state diagram of the state
machine 800 is shown in FIG. 10.
Referring now to FIG. 10, the state machine starts out in state IDLE. In
state IDLE, the contents of the serial isolation register SROM.sub.--
DAT[15:0] are set to 0.times.0000. The signals INC.sub.-- ADR, SROM.sub.--
DI, FETCH16.sub.-- CLR and SROM.sub.-- CS are all set low. The signal
IDLE.sub.-- ST is set high to indicate that the state machine 800 is
currently idle. Since the signal SROM.sub.-- CS is low, the serial EEPROM
330 is not selected. When a signal FETCH16.sub.-- LAT (provided by logic
in FIG. 9) is asserted high, the state machine 800 recognizes that data is
being requested from the serial EEPROM 330. As a result, the state machine
800 transitions to state BEGIN, where the signal SROM.sub.-- CS is set
high to enable the serial EEPROM 330. The serial input SROM.sub.-- DI to
the EEPROM 330 is also set high. In state BEGIN, the signal IDLE.sub.-- ST
is set low to indicate that the state machine 800 is now active. On the
next positive edge of the clock SROM.sub.-- CLK*, the state machine 800
transitions to state OPCODE1, where the signal SROM.sub.-- DI is
maintained high and the signal FETCH16.sub.-- CLR is set high to reset the
signal FETCH16.sub.-- LAT. On the next rising edge of the clock
SROM.sub.-- CLK*, control proceeds to state OPCODE0, where the signals
SROM.sub.-- DI and FETCH16.sub.-- CLR are set low. From here on, all state
transitions of the state machine 800 are assumed to occur on the rising
edge of the clock SROM.sub.-- CLK*. Next, the state machine 800
transitions to state A7. In state A7, the serial input SROM.sub.-- DI of
the serial EEPROM 330 is set to the state of the most significant ROM
address bit SROM.sub.-- ADDR[7]. Control proceeds next to state A6, where
the serial input SROM.sub.-- DI is set to SROM.sub.-- ADDR[6]. Control
proceeds in subsequent cycles to states A5, A4, A3, A2, A1 and A0, in the
listed order, in which the serial input of the EEPROM 330 is set equal to
address signals SROM.sub.-- ADDR[5:0], respectively. This series of steps
effectively loads the address SROM.sub.-- ADDR[7:0] into the serial EEPROM
330. From state A0, the state machine 800 transitions to state DUMMY,
where the serial input SROM.sub.-- DI is set low, and the signal
INC.sub.-- ADR is set high to increment the ROM address SROM.sub.--
ADDR[7:0]. Initially the ROM address will start at zero and this state,
when repeated, causes the ROM address to step through the ROM. The ROM
address counter is not shown but is of conventional design. From state
DUMMY, control proceeds to state R15, where the serial output SROM.sub.--
DO of the EEPROM 330 is read into bit 15 of the serial isolation register,
SROM.sub.-- DAT[15]. In state R15, the signal INC.sub.-- ADR is reset low.
From state R15, control proceeds to state R14, where the serial output
SROM.sub.-- DO of the EEPROM 330 is loaded into bit 14 of the serial
isolation register, SROM.sub.-- DAT[14]. In subsequent cycles, control
proceeds to states R13, R12, R11, R10, R9, R8, R7, R6, R5, R4, R3, R2, R1
and R0, in that order, in which the signal SROM.sub.-- DO is loaded into
the remaining serial isolation register bits SROM.sub.-- DAT[13:0],
respectively. From state R0, control returns to state IDLE, where all the
signals are set to their initial states. It is also noted that when a
signal SM.sub.-- RST is asserted, control is returned from any state to
state IDLE. The signal SM.sub.-- RST is asserted high after a write to the
wake data register or on an assertion of the system reset signal RST*. In
the manner described above, 16 bits of data are retrieved from the serial
EEPROM 330 at the location indicated by the address SROM.sub.-- ADDR[7:0].
Returning now to FIG. 9A, the signal FETCH16.sub.-- LAT is provided by a D
flip-flop 810. The D flip-flop 810 is clocked on the rising edge of CLK,
and it is reset on the rising edge of the output of an OR gate 812. The
inputs of the OR gate are connected to the inverted state of the system
reset signal RST*, the signal SROM.sub.-- RST and the signal
FETCH16.sub.-- CLR. The signal SROM.sub.-- RST is asserted after a write
to the wake data register. The D input of the D flip-flop 810 is connected
to the output of an OR gate 808. The first input of the OR gate 808 is
connected to the signal FETCH16.sub.-- LAT, and its second input is
connected to the output of an AND gate 806. The AND gate 806 is connected
to a signal FETCH16 and to the signal SROM.sub.-- CLK*. Thus, if the D
flip-flop 810 is set high, it stays in a high state until reset. To set
the D flip-flop 810, the signals FETCH16 and SROM.sub.-- CLK* must both be
high. The signal FETCH16 is provided by an 0R gate 814, whose inputs are
connected to signal FETCH16.sub.-- ISO and signal FETCH16.sub.-- RES. The
setting of the D flip-flop 810 is qualified by the clock signal
SROM.sub.-- CLK* to ensure that a race condition does not occur in the
state machine 800 between the signals SROM.sub.-- CLK* and FETCH16.sub.--
LAT. The signal FETCH16.sub.-- ISO indicates that the serial identifier of
the audio/modem card 318 is to be retrieved from the serial EEPROM 330
during the expansion card isolation process. In the preferred embodiment,
the serial identifier is 8 bytes in length. The signal FETCH16.sub.-- RES
indicates that the systems resource data are to be retrieved from the
serial EEPROM 330 during a resource data read cycle. The signal
FETCH16.sub.-- ISO is provided by a D flip-flop 816, which is clocked by
the rising edge of CLK and is reset on the falling edge of a signal
SROMCNTL.sub.-- RST*. The signal SROMCNTL.sub.-- RST* is provided by an
AND gate 820, whose first input is connected to the system reset signal
RST* and second input is connected to the inverted state of the signal
SROM.sub.-- RST. The D flip-flop 816 is reset high to ensure that the
signal FETCH16.sub.-- LAT is asserted to the state machine 800 after a
reset cycle. The D input of the D flip-flop 816 is connected to the output
of a multiplexor 818. The I0 input of the multiplexor 818 is connected to
the signal FETCH16.sub.-- ISO. The I1 input of the multiplexor 818 is tied
high and its I2 input is tied low. The S1 input of the multiplexor 818 is
connected to the output of an AND gate 822, and its S0 input is connected
to the output of an AND gate 824. The inputs of the AND gate 822 are
connected to the signal FETCH16.sub.-- LAT and to the output of an
inverter 826. The input of the inverter 826 is connected to the output of
an AND gate 828, whose inputs are connected to the signal RD.sub.--
ISO.sub.-- D, the inverted state of the signal RD.sub.-- ISO and to the
signal ISO.sub.-- CYCLE. The signal RD.sub.-- ISO, when asserted high,
indicates that a read is being performed to the serial isolation register
located in the state machine 800. The signal RD.sub.-- ISO.sub.-- D is
equivalent to the signal RD.sub.-- ISO delayed by one CLK cycle. The
signal ISO.sub.-- CYCLE indicates the phase of the serial isolation
register read cycle during the isolation process. Thus, the AND gate 828
outputs a 1 high CLK cycle after the isolation read signal RD.sub.-- ISO
has reset low and when the second phase of the serial isolation register
read cycle is in progress. If the signal FETCH16.sub.-- LAT is high and
the output of the AND gate 828 is low, the D flip-flop 816 is latched with
the value 0. This ensures that the signal FETCH16.sub.-- ISO is reset low
after the isolation process has completed. The output of the AND gate 828
is also connected to the first input of the AND gate 824. The second input
of the AND gate 824 is connected to the output of a comparator 830, which
compares the value of the pointer BITPTR[3:0] to the value 0.times.F. If a
match occurs, indicating that 16 bits have been read from the serial
isolation register, the comparator 830 outputs a 1, and if the output of
the AND gate 828 is also high, the AND gate 824 causes the D flip-flop 816
to be set high.
The pointer BITPTR[3:0] is provided by a register 802, which is clocked on
the rising edge of CLK and is reset on the falling edge of the signal
SROMCNTL.sub.-- RST*. The D input of the D flip-flop 802 is connected to
the output of a four bit, three input multiplexor 832, whose I0 input is
connected to the pointer BITPTR[3:0], whose I1 input is connected to
0.times.0, and whose I2 input is connected to the 4-bit output of an
increment circuit 834. The S1 input of the multiplexor 832 is connected to
the output of an AND gate 825, and its $2 input is connected to the output
of the AND gate 824. Thus, when the AND gate 824 drives its output high,
the value 0.times.0 is loaded into the register 802. The inputs of the AND
gate 825 are connected to the output of the AND gate 828 and to the
inverted state of the output of the comparator 830. Thus, if the signals
BITPTR[3:0] are not equal to 0.times.F and the output of the AND gate 828
is high, then the multiplexor 832 selects the output of the increment
circuit 834. This causes the signals BITPTR[3:0] to be incremented by 1
and latched into the register 802. The net effect of the logic described
above is that during an isolation process, the value of the pointer
BITPTR[3:0] is incremented once in each pair of reads to the serial
isolation register.
As described earlier in FIG. 8, the signal ISOKEY is required to determine
the current state of a selected bit of the serial identifier during the
isolation process. The signal ISOKEY is assigned to the data value
SROM.sub.-- DAT[BITPTR[3:0]] by a latch 836. The signal is reassigned
whenever either the signals BITPTR[3:0] or SROM.sub.-- DAT[15:0] change
state. As noted above, the pointer BITPTR[3:0] points to the current
location of the serial isolation register.
During the resource data read stage, the system BIOS expects the resource
data to be outputted one byte at a time. Since the serial isolation
register, which is also used to store the system resource data, consists
of 16 bits of data, a signal is required to indicate which half is to be
provided to the system BIOS. That function is provided by a signal
LOW.sub.-- BYTE, which is connected to the output of an AND gate 840. The
inputs of the AND gate 840 are connected to signals LOW.sub.-- BYTE.sub.--
ISO and LOW.sub.-- BYTE.sub.-- RES. Thus, whenever both the signals
LOW.sub.-- BYTE.sub.-- ISO and LOW.sub.-- BYTE.sub.-- RES are deasserted
high, the signal LOW.sub.-- BYTE is deasserted high to indicate a high
byte. The signal LOW.sub.-- BYTE.sub.-- ISO is provided to ensure that,
after the isolation process has completed reading the 8 bytes of the
serial identifier, the first read of the resource data from the isolation
register is from the high byte.
The signal LOW.sub.-- BYTE.sub.-- ISO is provided by a D flip-flop 842. The
D flip-flop 842 is clocked on the rising edge of CLK and is reset high on
the falling edge of the signal SROMCNTL.sub.-- RST*. The D input of the D
flip-flop 842 is connected to the output of a multiplexor 844. The I0
input of the multiplexor 844 is connected to the signal LOW.sub.--
BYTE.sub.-- ISO, the I1 input is tied high and the I2 input is tied low.
The S1 input of the multiplexor 844 is provided by the output of an AND
gate 846, and the SO input is provided by the output of an OR gate 850.
The inputs of the OR gate 850 are connected to the output of an AND gate
848 and the output of an AND gate 852. The first inputs of both AND gates
846 and 848 are connected to the output of the AND gate 828. The second
input of the AND gate 846 is connected to the output of a comparator 854,
and the second input of the AND gate 848 is connected to the output of a
comparator 856. The comparator 854 compares the value of BITPTR[3:0] to
0.times.7, and the comparator 856 compares BITPTR[3:0] to 0.times.F. The
first input of the AND gate 852 is connected to the output of the inverter
826 and the second input is connected to the output of an AND gate 858,
whose inputs are connected to signals RD.sub.-- RES.sub.-- D and RD.sub.--
RES. The signal RD.sub.-- RES being asserted high indicates that a read is
to be performed to the serial isolation register to obtain the system
resource data. The signal RD.sub.-- RES.sub.-- D is equivalent to
RD.sub.-- RES delayed by one CLK cycle. Thus, if the pointer BIT.sub.--
PTR[3:0] is equal to the value 0.times.7, and the AND gate 828 drives its
output high, the multiplexor 844 loads a 0 into the D flip-flop 842 to
indicate that the high half of the serial isolation register is about to
be accessed during the isolation process. However, if the pointer
BIT.sub.-- PTR[3:0] is equal to the value 0.times.F and the output of the
AND gate 828 is high, indicating that the low half of the isolation
register is about to be accessed, or if the outputs of the AND gate 858
and the inverter 826 are high, indicating that the isolation process has
ended and the resource data read cycle has begun, then the multiplexor 844
writes a 1 into the D flip-flop 842.
The signal FETCH16.sub.-- RES is provided by a D flip-flop 860 and the
signal LOW.sub.-- BYTE.sub.-- RES is provided by a D flip-flop 862. Both D
flip-flops 860 and 862 are clocked on the rising edge of CLK and are reset
on the falling edge of the signal SROMCNTL.sub.-- RST*. The D input to the
D flip-flop 860 is connected to the output of a multiplexor 864, whose I0
input is connected to the signal FETCH16.sub.-- RES, I1 input is tied low
and I2 input is tied high. The S1 input of the multiplexor 864 is
connected to the output of an AND gate 866 and the SO input is connected
to the output of an AND gate 868. The first input of the AND gate 866 is
connected to the output of an OR gate 870, whose inputs are connected to
the inverted state of the signal LOW.sub.-- BYTE.sub.-- RES and the
inverted state of the signal LOW.sub.-- BYTE.sub.-- ISO. The second input
of the AND gate 866 is connected to the output of the AND gate 858. The
output of the OR gate 870 is also connected to the input of an inverter
872, whose output is connected to the first input of an AND gate 874. The
second input of the AND gate 874 is connected to the output of the AND
gate 858. The D input of the D flip-flop 862 is connected to the output of
a multiplexor 876. The I0 input of the multiplexor 876 is connected to the
signal LOW.sub.-- BYTE.sub.-- RES, the I1 input is tied low and the I2
input is tied high. The S1 input of the multiplexor 876 is connected to
the output of the AND gate 866 and the SO input is connected to the output
of the AND gate 874.
Thus, if both the signals LOW.sub.-- BYTE.sub.-- RES and LOW.sub.--
BYTE.sub.-- ISO are high, then the output of the OR gate 870 is low. If
the output of the AND gate 858 is also high, which indicates that a
resource data read cycle is occurring, then the multiplexor 876 loads a 0
into the D flip-flop 862, causing the signal LOW.sub.-- BYTE.sub.-- RES to
fall low. If either of the signals LOW.sub.-- BYTE.sub.-- RES and
LOW.sub.-- BYTE.sub.-- ISO is low, then the OR gate 870 outputs a 1. If
the output of the AND gate 858 is also high, then the multiplexor 864
loads a 1 into the D flip-flop 860 and the multiplexor 876 loads a 1 into
the D flip-flop 862. This indicates that the second byte of data is being
read from the lower half of the serial isolation register. As a result,
the signal FETCH16.sub.-- RES is asserted high to cause the OR gate 840 to
assert the signal FETCH16. The first input of the AND gate 868 is
connected to the output of an inverter 878, whose input is connected to
the output of the AND gate 858. The second input of the AND gate 868 is
connected to the signal FETCH16.sub.-- LAT. Thus, if the output of the AND
gate 858 is low and the signal FETCH16.sub.-- LAT is high, then the
multiplexor 864 writes a 0 into the D flip-flop 860 to reset the signal
FETCH16.sub.-- RES low after the resource data read cycle has completed.
Referring now to FIG. 11, a portion of the output circuitry of the
expansion card is shown. A 4-to-1 multiplexor 1000 drives signals
PNP.sub.-- DO[7:0], which are ultimately provided to the system data bus
SD[7:0]. The signals ISO and CONFIG are connected to the outputs of the
AND gate 1014 and the OR gate 1014, respectively. The S1 input of the
multiplexor 1000 is connected to the signal ISO and the $0 input is
connected to the signal CONFIG. The first input of the AND gate 1014 is
connected to the signal ISO.sub.-- ST and a second input is connected to
the inverted state of the signal ALT.sub.-- CSN.sub.-- SEL. The first
input of the OR gate 1016 is connected to the signal CONFIG.sub.-- ST and
the second input is connected to the ALT.sub.-- CSN.sub.-- SEL. Thus, if
the audio/modem card 318 is in the ISOLATION state, which is indicated by
the signal ISO.sub.-- ST being asserted high, and the card 318 is not in
one of the two alternative configuration modes, indicated by the signal
ALT.sub.-- CSN.sub.-- SEL being asserted high, the I2 input of the
multiplexor 1000 is selected. The I2 input is connected to the output of a
multiplexor 1004. The S1 input of the multiplexor 1004 is connected to the
output of an AND gate 1008, and the SO is connected to the output of an
AND gate 1010. The first inputs of the AND gates 1008 and 1010 are
connected to a signal ADR.sub.-- SER.sub.-- ISO, which indicates when
asserted that the serial isolation register is being addressed during the
isolation process. The second input of the AND gate 1008 is connected to
the inverted state of the signal ISO.sub.-- CYCLE. The second input of the
AND gate 1010 is connected the signal ISO.sub.-- CYCLE. If the output of
the AND gate 1008 is high, then the multiplexor 1004 drives the value
0.times.55 through the multiplexors 1000 and 1004. However, if the output
of the AND gate 1010 is high, then the multiplexor 1004 drives the value
0.times.AA. Thus, during the first phase of the isolation register read
cycle during the isolation process, the multiplexor 1004 drives the value
0.times.55. During the second phase, the multiplexor 1004 drives the value
0.times.AA.
If the audio/modem card 318 is in the CONFIG state, as indicated by the
signal CONFIG.sub.-- ST being asserted high, or if one of the alternative
configuration modes indicated by the signal ALT.sub.-- CSN.sub.-- SEL is
asserted high, the OR gate 1016 selects the I1 input of the multiplexor
1000. The I1 input of the multiplexor 1000 is connected to the output of a
multiplexor 1006. If the serial isolation register is being addressed
during the resource data read cycle, a signal ADR.sub.-- RESDAT is
asserted high. This selects the I1 input of the multiplexor 1006, which is
connected to the output of a multiplexor 1012. The multiplexor 1012 is
selected by the signal LOW.sub.-- BYTE. Thus, if the signal LOW.sub.--
BYTE is low, the upper half of the serial isolation register SROM.sub.--
DAT[15:8] is provided to the latch 1002. If the signal LOW.sub.-- BYTE is
high, however, the lower byte of the serial isolation register SROM.sub.--
DAT[7:0] is provided to the latch 1002.
The default input of the multiplexors 1012, 1006 and 1000 are tied to the
value 0. It is noted that other signals are provided to the inputs of the
multiplexor 1006, which are selected by corresponding select signals.
Those signals are not shown for the sake of clarity.
Referring now to FIG. 12, the second embodiment of the present invention is
shown. This embodiment also removes the need for a separate serial EEPROM
330 associated with the audio/modem card 318. A static random access
memory (SRAM) 1100 is placed on the audio/modem card 318 to receive the
serial identifier and the system resource data from the system BIOS. The
system BIOS retrieves the serial identifier and the resource data from a
storage device, preferably the BIOS ROM 324, and writes it into the SRAM
1100 before the Plug and Play configuration process is executed. The SRAM
1100 is organized as 128 words by 16 bits, and is addressed by the output
of a 7-bit counter 1102. The output of the counter 1102 is designated as
address signals SRAM.sub.-- ADDR[6:0]. Because the audio/modem card 318 is
connected only to an 8-bit data bus SD[7:0], a register 1104 is provided
to store the lower byte of the data input, represented as data signals
D[7:0], into the SRAM 1100. The upper byte of the data input, represented
as data signals D[15:8], is provided by an 8-bit buffer 1106. The D input
of the register 1104 and the input of the 8-bit buffer are both connected
to the data bus SD[7:0]. The clock input of the register 1104 is provided
by the Q output of a D flip-flop 1110. The D input of the D flip flop 1110
is connected to its Q* output. Thus, the D flip flop 1110 effectively
functions as a toggle flip flop. The clock input of the D flip-flop 1110
is connected to the output of an AND gate 1108, whose inputs are connected
to the signals WRT.sub.-- WRITE.sub.-- PORT and ALT.sub.-- CSN.sub.-- SEL.
The signal ALT.sub.-- CSN.sub.-- SEL is included to ensure that the write
operation to the SRAM 1100 occurs only if an alternative configuration
mode is selected. The D flip flop 1110 is set to a high state on the
falling edge of the output of an AND gate 1112, whose inputs are connected
to the inverted state of the signal WAIT.sub.-- CMD and the signal
SROMCNTL.sub.-- RST*. The Q output of the D flip flop 1110 is connected to
the clock input of a D flip flop 1114, which is similarly configured as a
toggle flip flop. The D flip flop 1114 is set high on the falling edge of
the output of an AND gate 1116, whose inputs are connected to the signal
SROMCNTL.sub.-- RST* and WRT.sub.-- WRITE.sub.-- PORT. The Q output of the
D flip flop 1114 is connected to the write enable input of the SRAM 1100.
If the output of the D flip flop 1114 is asserted low, then the SRAM 1100
can be written through its data input D[15:0] at a location determined by
the counter 1102. The output of the D flip flop 1114 is also connected to
an input of an AND gate 1118, whose other input is connected to the
inverted state of the signal FETCH16.sub.-- LAT. The output of the AND
gate is provided to the clock input of the counter 1102. The counter 1102
is reset on the falling edge of the output of an AND gate 1136, which
receives the SROMCNTL.sub.-- RST* signal at one input. The second input is
provided by the output of a NAND gate 1134. The NAND gate 1134 receives
the inverted output of a D-type flip-flop 1132 and the non-inverted output
of a D-type flip-flop 1130, which is also connected to the D input of the
flip-flop 1132. The D input of the flip-flop 1130 receives the ALT.sub.--
CSN.sub.-- SEL signal. The flip-flops 1130 and 1132 are clocked by the CLK
signal.
Thus, when the two signals WRT.sub.-- WRITE.sub.-- PORT and ALT.sub.--
CSN.sub.-- SEL are asserted high, the AND gate 1108 asserts a 1 at its
output, causing the D flip flop 1110 to toggle low. This causes the D flip
flop 1104 to latch in the data on the data bus SD[7:0]. On the next rising
edge of the signal WRT.sub.-- WRITE.sub.-- PORT, the D flip flop 1110
toggles high, causing the D flip flop 1114 to toggle low. The write enable
input of the SRAM 1100 is thus driven active low, and the lower and upper
bytes of data presented by the D flip flop 1104 and the buffer 1106 are
written into the SRAM 1100. When the signal WRT.sub.-- WRITE.sub.-- PORT
next falls low, the output of the AND gate 1116 is driven low to reset the
D flip flop 1114 high, thereby disabling the write enable input of the
SRAM 1100. However, at the same time, the output of the OR gate 1118 is
driven high, causing the counter 1102 to increment. Thus, the next write
access will be to the next word in the SRAM 1100. This process is
continued until the serial identifier and all the system resource data
have been written to the SRAM 1100. After the final write to the SRAM
1100, the system BIOS issues a WAIT FOR KEY command, represented by the
assertion of the signal WAIT.sub.-- CMD, to place the Plug and Play logic
351 into the WAIT FOR KEY state.
The serial identifier and resource data can thus be retrieved from the SRAM
1100 during the Plug and Play configuration mode. In the second
embodiment, the asserted signal ALT.sub.-- CSN.sub.-- SEL disables the
state machine 800, which provides the serial identifier and resource data
via signals SROM.sub.-- DAT[15:0] during the standard configuration mode.
The serial identifier and resource data are read from the SRAM 1100 and
provided to an alternative 16-bit serial isolation register 1122, which
outputs signals SRAM DAT[15:0]. The output enable input of the SRAM 1100
is provided by an inverter 1124, whose input is connected to the signal
FETCH16.sub.-- LAT. When the signal FETCH16.sub.-- LAT is asserted, the
inverter 1124 enables the SRAM 1100 to be read. The signal FETCH16.sub.--
LAT is also provided to the select input of a multiplexor 1128, whose I1
input is pulled to ground and I2 input is tied high. The output of the
multiplexor 1128 is connected to the D input of a D flip flop 1126. The D
flip flop 1126 is clocked on the falling edge of the signal SROM.sub.--
CLK* and is reset by the signal SROMCNTL.sub.-- RST*. If the signal
FETCH16.sub.-- LAT is asserted high, the D flip flop 1126 is set high on
the falling edge of the signal SROM.sub.-- CLK*. This drives the signal
FETCH16.sub.-- CLR, which is provided to the D flip flop 810 (FIG. 9A) to
reset the signal FETCH16.sub.-- LAT low. When the signal FETCH16.sub.--
LAT is reset, the next falling edge of the signal SROM.sub.-- CLK* causes
the signal FETCH16.sub.-- CLR to reset low. The falling edge of the signal
FETCH16.sub.-- LAT also causes the counter 1102 to increment.
The output data from the SRAM 1100, represented by signals Q[15:0], are
loaded into the register 1122 on the next rising edge of CLK. The pointer
BITPTR[3:0] is provided to the register 1122 to point to the current bit
of the register 1122 in an isolation register read cycle during the
isolation process. The output of the register 1122 is connected to the I1
input of a 2-to-1 multiplexor 1130. The I0 input of the multiplexor 1130
is connected to the signals SROM.sub.-- DAT[15:0] from the isolation
register in the state machine 800. The select input of the multiplexor
1130 is connected to the signal MODE.sub.-- 1.sub.-- OR.sub.-- 2. Thus, if
Plug and Play logic 351 is placed into either first or second alternative
configuration modes, the output of the register 1122 is selected, wherein
the lower byte is provided to the I0 input of a multiplexor 1012' and the
upper byte is provided to its I1 input. In the second embodiment, the
multiplexor 1012' replaces the multiplexor 1012 of FIG. 10. Also, in FIG.
5, the input of the OR gate 406 that was connected to the signal
ALT.sub.-- CSN.sub.-- SEL is tied to ground. The second embodiment thus
places the serial identifier and resource data into an SRAM 1100 located
on the audio/modem card 318. Additionally, the output of the multiplexor
1130 is provided to the isolation key latch 836 so that the ISOKEY signal
can be properly developed. Further, the ISO.sub.-- ST and CONFIG.sub.-- ST
signals are provided directly to the select inputs of the multiplexor
1000. Also, the output of the NAND gate 1134 is used to reset the register
816. After the data is properly written, a zero value is written to the
register 402 to deassert the ALT.sub.-- CSN.sub.-- SEL signal, so that
data cannot be written to the SRAM 1100. The Plug and Play configuration
process is then invoked, wherein the system BIOS performs the key
initiation, the isolation process, the CSN assignment, and the
configuration register programming. Therefore in this second embodiment
the SRAM 1100 then emulates the serial EEPROM 330 during the Plug and Play
isolation and configuration process.
Thus, a circuit has been described that allows a Plug and Play expansion
card to be configured in one of three ways. The first is the standard Plug
and Play configuration method, wherein expansion cards go through the
isolation process to obtain unique Card Select Numbers (CSN) using a
dedicated serial EEPROM to store the serial identifier and system resource
data for the expansion cards. However, when an expansion card is directly
mounted onto a system board, it becomes a system board device. This allows
the separate serial EEPROM to be removed. To implement this case, two
embodiments, each with two alternative configuration modes are provided,
wherein the expansion card can be configured under main CPU control. In
these alternative modes, the configuration data is stored in the main
system BIOS ROM. In the first mode, a register in the expansion card is
mapped to a fixed ISA I/O address. In the second mode, the register is
controlled by a dedicated pin, thus allowing it to be mapped to any ISA
I/O address. To determine which configuration mode is used by the
expansion card, pullup or pulldown resistors are connected to certain
expansion card output pins. In the first embodiment, the configuration
data is written directly into the configuration registers without
requiring the Plug and Play isolation and configuration process. In the
second embodiment a static random access memory (SRAM) is utilized to
store the serial identifier and the resource data. In this embodiment, the
system BIOS initially writes the serial identifier and resource data into
the SRAM. After this is done, a Plug and Play configuration process is
invoked, in which the serial identifier is retrieved from the SRAM rather
than the serial EEPROM.
The foregoing disclosure and description of the invention are illustrative
and explanatory thereof, and various changes in the size, shape,
materials, components, circuit elements, wiring connections and contacts,
as well as in the details of the illustrated circuitry and construction
and method of operation may be made without departing from the spirit of
the invention.
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